Identification and localization of connexin26 within the photoreceptor-horizontal cell synaptic complex

Connexin26 (Cx26) is a member of the family of integral membrane proteins t hat normally form intercellular gap junctional channels. We have used Weste rn blotting, immunofluorescence, immunoelectron microscopy, and single-cell reverse-transcriptase polymerase chain reaction amplification IRT-PCR) to analyze the expression and cellular localization of Cx26 in the carp retina . In the outer plexiform layer, strong clustered Cx26 immunolabeling was co ncentrated at and restricted to the terminal dendrites of horizontal cells. Single-cell RT-PCR confirmed the expression of Cx26 in carp retinal horizo ntal cells. 248-bp fragments amplified fr om cDNAs of Foul different horizo ntal cells were cloned and each nucleotide sequence encodes a protein fragm ent (AA 104-185) with highly significant homology to rat and mouse Cx26. im munoelectron microscopy revealed that only the invaginating dendrites of ho rizontal cells in intimate lateral association with the presynaptic ribbon complex were labeled. No labeling was found at the photoreceptor membrane a nd there was no septalaminar structure, indicative of gap junctions, betwee n photoreceptors and horizontal cells. The focal location of Cx26 at the me mbrane of the dendritic tips of horizontal cells and the lack of gap juncti onal morphology suggests that Cx26 might form hemichannels.